Peruvian protector

If current European corn borer (ECB) control options frustrate you, go south. Way south. Peru — the northwestern South American country best known for mountains, coffee and sugarcane — may hold the answer to your corn borer battle.

USDA Agricultural Research Service scientists have discovered a Peruvian germ-plasm line that naturally deters ECB. If plant breeders someday incorporate the germ plasm into a commercially viable corn hybrid, farmers could glean ECB resistance without the drawbacks of current control options, says Craig Abel, research entomologist at the USDA Southern Insect Management Research Unit, Stoneville, MS.

Fewer headaches. Many farmers currently plant Bt hybrids to deter ECB, which damages $1 billion of corn annually throughout the U.S. Yet Bt corn has several disadvantages. To reduce the chance of ECB resistance to Bt corn, farmers must plant non-Bt corn refuges that border Bt fields. They must also pay a technology fee for Bt corn.

The alternative to Bt corn for ECB control isn't pretty, either. Insecticides often fail to control ECB because just a short treatment time exists before larvae bore into corn stalks.

If the Peruvian germ plasm were incorporated into a commercially available hybrid, farmers would avoid insecticide application drawbacks. Because the germ plasm would be publicly developed, farmers would not need to pay a technology fee. They also could avoid Bt corn's refuge requirement.

“You'd also avoid a lot of the marketing problems that GM [genetically modified] grains have,” Abel adds. “You wouldn't have to worry if your elevator will buy your grain.”

Unique resistance. The resistant germ-plasm line — GEMS-0001 — originated in northern Peru, where sugarcane borer (SCB) devastates both corn and sugarcane. Abel believes that indigenous farmers may have selected corn containing the germ plasm for SCB resistance. Because SCB and ECB have similar feeding habits, cross-resistance between the two pests may have occurred.

In 1991 and 1992, Abel evaluated 1,600 corn germ-plasm lines from this area. Out of these, 11 had ECB resistance.

“This type of resistance was unique,” Abel says. “There's a substance called dimboa, a natural chemical that spurs resistance to European corn borer. These lines have low levels of dimboa, so something else is spurring resistance.”

USDA researchers used GEMS-0001 as a donor parent to infuse the resistance trait into two public inbred lines developed by Iowa State University plant breeders.

“We still don't know what chemical the germ plasm contains,” Abel says. “But it has a sublethal effect on European corn borer. It doesn't outright kill them, but instead greatly slows larval development.”

Typically, ECB larvae feed on leaf tissue before boring into the stalk. But in the case of GEMS-0001, few borers proceed into the stalk after leaf feeding.

“The inhibiting factor is in the leaf, leaf sheath and collar,” Abel explains. “They just don't like it.”

In development. USDA researchers have released GEMS-0001 for seed companies to use in their breeding programs. “We've developed inbred lines from GEMS-0001 that are fixed for resistance,” Abel says. “We now have to go back and pick lines with no yield drag.” Abel says that such hybrids probably won't be commercially available for at least seven years.